This application relates generally to data transmission, and more particularly to data transmission over power lines.
The use of power lines to transmit data is known. Initially, powerline communication systems were limited to relatively low data rates, typically less than 500 kbs. These low data rates are generally useful for applications such as remote control of various switches connected to the powerline system. More recently, developments have been made in the area of broadband powerline communication systems, also known as powerline telecommunications (PLT) systems or broadband powerline (BPL) systems. These systems are capable of transmitting data at significantly higher data rates than previous systems. For example, BPL systems can transmit data at rates of 4–20 Mbps.
While existing powerline systems are capable of transmitting data at the rates described above, they were not initially designed for data transmission. Instead, they were designed to carry large currents at high voltages so that significant amounts of energy could be distributed at one primary low frequency (e.g., 60 Hertz).
Powerline communication systems generally use one or more carrier frequencies in order to spread the data transmission over a wider range of frequencies. The low data rate powerline communication systems discussed above generally utilized frequencies in the range of 9 kHz to 525 kHz. In these low data rate systems, the risk of interference from external radiation sources is low. The high data rates of BPL systems cannot be achieved using carrier frequencies below 525 kHz. Instead, BPL systems typically use carrier frequencies in the range of 1–30 MHz.
One of the problems with a BPL system is the detrimental effects of inbound interference from external electromagnetic radiators. The physical attributes of the power lines (e.g., high elevation and unshielded wiring) along with the higher carrier signal frequencies needed for high bandwidth data transmission, contribute to this interference problem.